Chebyshev centres and centrable sets

In this paper we characterize real Banach spaces whose duals are isometric to $L^1(\mu)$ spaces (the so-called $L^1$-predual spaces) as those spaces in which every finite set is centrable. For a locally compact, non-compact set $X$ and for an $L^1$-predual $E$, we give a complete description of the extreme points and denting points of the dual unit ball of $C_0(X,E)$, equipped with the diameter norm.